► Major facelift for S-class saloon► Driven in various specs► Still the luxury car king?

Luxury saloons may only represent a small portion of the car market but it’s a hugely important part, due to the huge amount of new technology that makes its debut. With a still-impressive BMW 7-series, plus a fresh Audi A8 and Lexus LS.

The Mercedes S-class was facelifted towards the end of 2017 but this is far more than just a facelift, including 1600 new components. It’s the first car to get Mercedes’ new inline-six petrol and diesel engines and revised V8 petrols.

Some of the driver assistance equipment now fitted to the S-class is already on the E-Class, but some is new. In a fast-evolving field, the tech is close to the limit of what is currently permitted by law; it will drive for you in certain circumstances, but you need to stay alert and ready to retake full control at any moment.

What’s in the S-class range?

The UK line-up has expanded since the current car first arrived in 2017 (essentially a new model, if strictly speaking a massive facelift for the 2014 model). All are long-wheelbase-only except the entry-level 350d, which is also available with with a 130mm-shorter wheelbase.

And now there’s a plug-in hybrid, the S560e L EQ Power, a 3.0-litre V6 making 362bhp plus 121bhp from the electric motor, for a total system output of 470bhp.

All are rear-wheel drive (in the UK) and have a nine-speed automatic, except the S65, which has a seven-speed auto.

Prices start £75,285 for the S350d; there’s a big leap to £97,480 for the plug-in hybrid; and another big leap for the AMGs, with the S65 AMG priced at £189,260 on the road.

Talk me through the S500 engine

It’s the most innovative engine in the range, making 429bhp and 384lb ft. It has a 48-volt electrical system supplementing the conventional 12-volt system. Instead of a conventional alternator, it has an integrated starter-generator (designed into the engine from the off, with no drive belt, making it compact).

This performs many functions, including powering an electric booster to give quick bursts of assistance to the engine to overcome any turbo lag. It provides the power for energy-sapping items such as the water pump and air-con compressor, giving consistent air-con performance whether the car is moving or stationary. It regulates the engine idle, allows a more sophisticated start-stop system and it's integral to the braking energy recuperation system

This is a 'systematically electrified' engine – an inelegant phrase employed to avoid any confusion with the impending plug-in hybrid with an electric-only range of up to 30 miles.

Start it up and you’re greeted by hardly any aural or physical intrusion into the cabin; you sort of expect that from a £100k+ luxury car anyway, but the S500 wakes up in an almost eerily silent way.

Give it a bootful and progress is suitably strong but unlike the diesel, this straight-six petrol needs to be revved out to get to the juicy bit of power at the top end. That’s almost an entirely different way of doing things to the low-rev, torque-focused S350d and as much as the S500 has a tuneful growl, the whole point of the S is to waft and surge effortlessly – not resorting to dropping cogs and making the engine scream.

And now there's a hybrid version too

The third-generation S-Class hybrid should get an extra-wide bootlid to cope with its full name: S560e L EQ Power. It’s available in just the one trim level, AMG Line, like all the non-AMG S-Classes.

As is usual with hybrids, the electric motor is fed by a battery, which is in turn fed by the engine, by braking and by plugging it in to the grid. What’s less usual is how seamlessly and effectively the petrol engine and electric motor work together. This is in large part down to Merc’s Eco Assist system, which employs some very joined-up thinking. It draws on the car’s many sensors and its highly advanced sat-nav to anticipate opportunities for gliding along with the engine off, for instance when going downhill or approaching slow-moving traffic. An icon flashes up to suggest you lift off. If you do, the system’s algorithms will decide between gliding, braking, petrol propulsion or electric propulsion, and it will use the ISG (integrated starter generator) to fire the engine back up in the precise split second when it will be most useful.

Eco Assist is not unique to the hybrid, but it does seem to be very much at home here. You have an all-electric range of up to 30 miles; using a wallbox you can charge the battery to full in two hours. The 13.5kWh battery is physically smaller than the previous generation, but still eats into boot space, down to 410 litres from the 510 available in most S-Classes.

It accelerates to 62mph in 5.0sec, which is 0.1sec quicker than the 450, despite being 200kg heavier, or 0.2sec slower than the S500.

The offical consumption figures are skewed by the plug-in element to a meaningless 104.6-128.4mpg. In reality, how much petrol you use will vary massively depending on how much driving you do using electricity from the grid. But however you drive, the hybrid has clear financial benefits: by far the cheapest road tax of any S-Class (£15 vs £515 for the next-best S450 and 500), by far the best BiK tax rate (16 per cent vs 34 per cent), and it’s the only one that’s London congestion charge exempt.

The hybrid dimension brings out what’s already there in the S-Class: it’s a thinking car, always aiming for efficiency, smoothness, safety. The S63 is dynamically sharper, whereas all the others are, like the 560e, best enjoyed wafting around. As well as the changes brought by your right foot, you also have a choice of driving modes. Eco mode makes the throttle action feel unnatural; Sport is over-eager; Normal is a fine compromise.

You can access a welter of information about what’s going on near-silently under the bonnet in terms of power drain and consumption, but once the novelty of monitoring the flow of electricity has worn off you find yourself just trusting it to take care of business, while you enjoy some heavyweight wafting.

So, this assistance tech… what’ll it do?

Much of it is focused on making your driving experience smoother, simpler and more relaxing. Think of it as being the best cruise control system imaginable.

Your S-class will follow other traffic at a safe distance (the distance itself can be adjusted by the driver), speeding up and slowing down without you touching the pedals. It will slow down for bends; the degree to which it slows is influenced by which of the dynamic modes you’re in. It will also change lane for you; you just indicate at a suitable moment and it will move out, pass and move back in.

All of this depends on various factors, chiefly the type of road. If you’re on a motorway with clear markings easily read by the cameras and radar (backed up by GPS and built-in mapping) then it will usually work, although even then it will demand that you prove that you’re not napping by clutching the steering wheel every few seconds. If you’re on a country road, it’s less likely to function. But the transition between working and not working soon becomes natural, with a system of lights and beeps making it readily obvious who’s driving.

Road Surface Scan is technology that's been fitted since 2013, but a newly upgraded stereo camera now scans more thoroughly, over a longer distance, at higher speeds, in darker conditions, meaning it works more effectively – in conjunction with sat-nav data and built-in mapping – to help the driver. For instance, it can slow down when you're nearing a toll booth or a motorway exit. And, cleverly, if it spots that you're approaching a queue of traffic that has started to move, it will aim to slow down and match the queue's speed rather than come to a halt and then pull away again.

The car’s self-parking ability is hugely impressive too. It will check whether a space is suitably big, and then once you’ve confirmed that you want to park it'll handle everything else for you, whether it’s parallel or perpendicular, forwards or backwards. And then it will get you out again. It goes much, much closer to parked vehicles than you’d dare (and doesn't beep at you, which it would if you were parking manually).

The other group of aids, the stuff designed to avoid (or reduce the impact of) accidents, was vividly demonstrated for us on an airfield. A variety of static and moving dummies, and a moving mock-up car, showed the S-class’s prowess at knowing when to emergency brake for you, when to help you steer around a pedestrian, and when to carry on.

Verdict

Is the S-class a car for driving or being driven in? Both. All the new S-classes maintain the excellence of previous versions, while benefitting from some very impressive electronic aids and the petrol engine in this S500 is a technological triumph.

In the back, in the long-wheelbase version, it’s roomy, relaxing and has a wealth of climate, massage and infotainment systems for you to play with, while at the front it's superbly comfortable and easy to drive, if (obviously) a bit on the large side.

With the S500 in particular - as much as it’s a clever engine, we do wonder if there’s much point when the ‘entry-level’ S350d suits the laid-back driving style of the S better, and gets slightly better fuel economy to boot but, regardless, the big S is still a wonderful luxury car

All the versions of current S-Class we’ve driven have been excellent, with the emphasis on sharper handling and firmer ride in the AMG models and on fuel-efficiency in the plug-in hybrid. The S500 is an excellent long-distance limo, as is the hybrid, but the 350d has almost all the same qualities but at a considerably lower initial outlay.